1. Field of the Invention
The present invention relates to a pneumatic tire that can reduce an electric resistance and improve the safety in use.
2. Description of the Background Art
In recent years, various methods have been proposed using silica for example in the tread part of a tire, and furthermore also in the breaker part and the sidewall part as other members of the tire in order to reduce the rolling resistance of the tire and to maintain wet grip performance. However, in the case of compounding silica in a large amount, the electric resistance of the tire increases and for example there is a case that a spark due to static electricity is generated and fuel is ignited when fuel is supplied to a vehicle, and there is a problem that safety cannot be assured when used. Therefore, there is demand to supply a tire realizing a reduction of the rolling resistance and maintaining wet grip performance that is capable of preventing the generation of static electricity.
With respect to such a pneumatic tire that can improve the conductivity and prevent a discharge phenomenon caused by accumulation of static electricity in the vehicle body, Japanese Patent Application Laid-Open No. 08-230407 has proposed a pneumatic tire in which: a rubber composition forming a tread section is allowed to contain 50 parts by weight or less of carbon black per 100 parts by weight of rubber component, with a non-carbon black based reinforcing agent being contained therein; a rubber composition forming a sidewall section is allowed to contain 40 parts by weight or less of carbon black per 100 parts by weight of rubber component; conductive thin films are affixed to the tread section and the sidewall section, with the rubber composition forming the conductive thin film having a compounding amount of carbon black of 60% by weight or more per 100 parts by weight of rubber component and being set to 35% by weight or more with respect to the entire rubber composition.
In an attempt to provide a pneumatic tire that can effectively reduce the tire electrical resistance while maintaining a superior wet performance, and also can exert these characteristics stably from the initial state of use to wear limit, Japanese Patent Application Laid-Open No. 2000-190709 has proposed a pneumatic tire in which: a tread rubber, constituted by a main tread rubber section made from an insulating rubber material cross-linked by silica, having a volume resistivity of 1×108 Ω·cm or more and an outer conductive section that is made from a conductive rubber member having a volume resistivity of less than 1×108 Ω·cm, forms a ground-contacting face together with the main tread section, and starts from the end edge of the ground-contacting face and ends with a distance of 3 to 35% of the ground-contacting width being interposed therebetween from the end edge of the ground-contacting face inward in the tire axial direction, and the outer conductive section, which has a sheet shape with a thickness in a range from 0.01 to 1.0 mm, is exposed to the outer face of the tread containing a groove wall and a groove bottom of a lateral groove, and continues in the tire circumferential direction, and a wing rubber, a sidewall rubber and a clinch rubber are formed by using a conductive rubber material, with the outer conductive section being connected to the wing rubber.
In an attempt to provide a rubber composition for a tire sidewall that has a low rolling resistance, is superior in abrasion resistance and wet performance and provides a tire having a low electrical resistance, Japanese Patent Application Laid-Open No. 10-036559 has proposed a rubber composition for a tire sidewall which is obtained by adding 5 to 50 parts by weight of carbon black having a primary particle size of 20 nm or more, a compression DBP oil absorption of 120 ml/100 g or less and a CTAB surface area of 130 m2/g or less, 10 to 60 parts by weight of precipitation silica having a DBP oil absorption of 200 ml/100 g or more and a BET nitrogen adsorption specific surface area of 180 m2/g or less and silane coupling agent setting to such an amount whose reactive factor is controlled within a specific range, to 100 parts by weight of specific diene-based rubber to be kneaded therein.
In an attempt to prevent a reduction in a conduction-preventive property in a tire tread using silica as a reinforcing agent, Japanese Patent Application Laid-Open No. 08-034204 has proposed a tire tread which is constituted by a strip made from a rubber composition for a tire tread having a high resistivity and extends in a length direction with a predetermined lateral width, and a conductive strip that is placed in the length direction within the lateral width and extended from the surface to the bottom face of the tread strip, and is formed by a low resistivity rubber composition for a tire having a volume resistivity of 108 Ω·cm or less.
In an attempt to provide a rubber composition for a tire tread capable of preventing static electricity accumulating in the vehicle body, Japanese Patent Application Laid-Open No. 10-147668 has proposed the rubber composition for a tire tread formed by compounding 1.0 to 30 parts by weight of a compound having an oxyethylene unit, 5 to 80 parts by weight of silica, and 0 to 40 parts by weight of carbon black per 100 parts by weight of a rubber constituent consisting of a diene rubber However, in the methods of Patent Documents 1 to 5, there is still enough room for improvement in the respect of highly managing to have low electric resistance and high safety at the same time to a sufficiently satisfactory level.